Stick insects mimicked ancient plants millions of years ago, according to a new study of fossils. The remarkable defense was developed soon after birds first took to the skies.
Fossilized remains of Cretophasmomima melanogramma insects and plants show the adaptation is at least 126 million years old. Relatives of these species have been discovered that are even older than that, but none developed the same ability to disguise themselves as vegetation.
"Our discovery demonstrates that plant mimicry by insects was achieved by various insect groups, including stick insects, before the rise of flowering plants," Olivier Bethoux of Sorbonne University, co-author of the study, told National Geographic.
Insects are rarely fossilized, so this find was a welcome discovery for both paleontologists and biologists. The fossils of Cretophasmomima melanogramma come from Mongolia. The name means "ancient black-lined stick insect." These valuable fossils were uncovered in northeast China's Jehol rock formation, located in Liaoning province.
Maomin Wang of Capital Normal University in Bejing led the investigation of the insect fossils. Two of the specimens were males, while another was female. They were each slightly less than three inches long. The fossils showed parallel black lines the stretching down the wings, disguising the body features as ginko leaves. That plant was common in Mongolia during that era.
Researchers theorize the wings were used to hide the body of the insect from predators. Even the color of the insect likely matched that of the ginko.
Melanogramma lived during the Cretaceous Era, at the end of reign of dinosaurs on Earth. Mongolia offered the insects a land full of conifers and plants. When early birds and highly-nimble mammals evolved, the insects evolved traits proving them camouflage among the vegetation.
"As early as in the Early Cretaceous, some stem-Phasmatodea achieved effective leaf mimicry, although additional refinements... were still lacking. The [greater numbers] of small-sized [tree-dwelling, insect-eating] birds and mammals might have triggered the acquisition of such primary defenses," researchers wrote in the study.
The connection between the ancient insects and the plants became apparent when a Cretophasmomima melanogramma was found in the same structure with a Membranifolia admirabilis, the ginko relative.
One of the best-known of the 3,200 modern species of stick insects is the praying mantis. Some are even kept as pets. They are often called walking sticks.
One variety, the Chan's megastick of Malaysia, is the world's longest insect, measuring up to 22" inches from head to tail.
